1. Technical Field
The present invention relates to a projection system that readily allows correction of aberrations produced due to a temperature change and a projection-type image display apparatus including the projection system.
2. Related Art
In a projection-type image display apparatus, such as a projector, the density of light rays that pass through a projection system increases as the luminance of light outputted from the apparatus increases. The temperature of a lens that forms the projection system therefore increases when an image is projected, resulting in a change in optical characteristics of the projection system in some cases.
JP-A-2016-80823 discloses a technology for correcting a change in the optical characteristics due to a temperature change by moving at least two lens groups out of a plurality of lens groups that form the projection system in the optical axis direction. One of the two lens groups, which is moved in the optical axis direction, corrects field curvature of a projected image degraded due to the temperature change. The other lens group, which is moved in the optical axis direction, corrects a back focus position of the projection system that changes due to the temperature change.
In the case where the temperature of a lens that forms the projection system increases when an image is projected, astigmatism, among the optical characteristics of the projection system, worsens in some cases.